Resonant Ultrasound Studies of Complex Materials: Clathrates and Transition Metal Oxides

* 非技术性摘要 * 现代凝聚态物理学最令人兴奋的主题之一是发现和研究不断增加的复杂材料系统中的新现象和新形式的秩序。所提出的计划的目标之一是研究弹性特性（即，材料如何响应应变）的新的、复杂的材料。将研究两种复杂材料：过渡金属氧化物和所谓的包合物（具有笼状结构的化合物）。后者有望开发更好的热电设备，将热量转换为电力（反之亦然），而无需移动部件或含氯氟烃（CFC）的制冷剂。这些复杂材料的弹性行为可能是相当奇特的，这项研究计划将探索在多大程度上可以理解的行为与最近发展的理论。高年级本科生和研究生都将在弹性性能和低温物理领域获得深入的经验，并将获得材料科学各种技术的技能。该提案包括为系内本科生开展外联活动。将特别努力帮助女学生。技术摘要 * 本研究项目旨在系统地研究复杂材料的弹性响应，包括过渡金属氧化物（TMO）和包合物。所研究的材料都是凝聚态物理的前沿材料，包括钙钛矿层状复合物Ca_（2-x）Sr_x）RuO_4，三角晶格化合物Na_x）CoO_2，包合物如YbFe_4 Sb_（12）和II型包合物如Rb_8 Na_（16）Si_（136）。将常规使用2-400 K的共振超声光谱法来获得弹性模量。将酌情在He 3低温恒温器中进行脉冲回波和衰减测量。从科学上讲，有许多问题需要解决。一个问题涉及包合物和结构玻璃之间的关系。具体地说，隧道状态是内含化合物所固有的吗？如果是，隧道实体是否可以识别？另一个问题涉及结构-性质关系。各种结构特征在多大程度上可以用来预测材料的性能？TMOs的弹性性质是否可以用最近发展的几何和其他类型的挫折，纳米尺度相分离和量子临界性的想法来理解？高年级本科生和研究生都将在弹性性能和低温物理领域获得深入的经验，并将获得材料科学各种技术的技能。该提案包括为系内本科生开展外联活动。将特别努力帮助女学生。

*** NON-TECHNICAL ABSTRACT ***One of the most exciting themes of modern condensed matter physics is the discovery and investigation of novel phenomena and new forms of order in materials systems of ever increasing complexity. It is one of the goals of the proposed program to study the elastic properties (i.e., how a material responds to strain) of novel, complex materials. Two kinds of complex materials will be studied: transition metal oxides and so-called inclusion compounds (compounds with a cage-like structure). The latter are promising for the development of better thermoelectric devices, which convert heat to electricity (and vice-versa) without moving parts or chloroflurocarbon (CFC)-containing refrigerants. The elastic behavior of these complex materials can be quite exotic, and this research program will explore to what extent the behavior can be understood with recently developed theories. Both senior undergraduate and graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to undergraduate students in the department. Special efforts will be made to reach female students.*** TECHNICAL ABSTRACT ***This research program is designed to systematically study the elastic response of complex materials, including transition metal oxides (TMOs) and inclusion compounds. The materials that will be investigated are at the forefront of condensed matter physics and include the layered perovskite ruthenates Ca_(2-x)Sr_(x)RuO_(4), the triangular lattice compound Na_(x)CoO_(2), and inclusion compounds such as YbFe_(4)Sb_(12) and type-II clathrates such as Rb_(8)Na_(16)Si_(136). Resonant Ultrasound Spectroscopy will be routinely used from 2-400 K to obtain the elastic moduli. Pulse-echo and attenuation measurements in a He3-cryostat will be performed as appropriate. Scientifically, there are a number of issues that need to be resolved. One issue involves the relationship between inclusion compounds and structural glasses. Specifically, are tunneling states intrinsic to inclusion compounds? If so, can the tunneling entities be identified? Another issue involves structure-property relationships. To what extent can various structural features be used to predict the properties of the material? Can the elastic properties of TMOs be understood with recently developed ideas involving geometric and other types of frustration, nano-scale phase separation, and quantum-criticality? Both senior undergraduate and graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to undergraduate students in the department. Special efforts will be made to reach female students.